A major benefit which results from providing stronger signals from satellite transmissions to earth based receivers is that smaller, less expensive, and simpler earth based satellite receive antennas ("dishes") can be employed. The use of smaller satellite dishes makes the use of satellite transmission more competitive with terrestrial transmission modes such as fiber, cable, etc., which will likely result in greater acceptance of satellite communications in general.
One technique for providing stronger satellite signals involves increasing the signal strength of the traveling wave tube (hereinafter referred to as "TWT") applied to each channel, or an increase in the number of TWTs of similar strength being applied to each channel, in an effort to produce a stronger signal being transmitted over each channel by the satellite. An increase in the signal strength being produced by each TWT typically requires a careful consideration of the cooling configuration, since a substantial portion of the energy associated with the production of the signal within each TWT is converted into heat energy which must be removed.
In recent decades, design considerations for satellites, and more particularly communication satellites, have included providing satellites with more power for each channel, and more channel transmission capabilities for each satellite. These considerations have frequently been balanced against other considerations which include the weight of the satellite. The greater the weight of the satellite (greater satellite operational lifetimes typically require satellites with a greater mass) generally the greater is the cost of the launch vehicle required for the satellite.
One component which is frequently used in communication satellites is the TWT which functions as the power amplifier. A traveling wave tube amplifier (hereinafter referred to as "TWTA") generally consists of a TWT plus its high voltage power supply (or electronic power conditioner, "EPC"). One design limitation of the TWT is that it generates a considerable amount of heat. Most high power communication satellites presently use conduction-cooled TWTs. The use of conduction cooled TWTs necessitates the use of heat spreaders and heat pipes to distribute the heat produced by the TWT, and large specialized radiating surfaces to transfer this waste heat into space. The thermal requirements, as well as the associated satellite weight and size limitations for launch on a given vehicle, further limit the number of high power TWTs which can be carried on a satellite of a given size.
Some TWTs are known to utilize one EPC for each pair of TWTs, this combination not only reduces overall power and amplifier weight but may provide other unrelated performance benefits. However, heat dissipation associated with TWTs remains a major limitation on the number of TWTs which each satellite is capable of carrying. This is generally true because the total heat dissipation capacity of a satellite is generally proportional to the size of the satellite.
A method to increase the heat dissipation capacity of a satellite is to employ TWTs which radiate a portion of the waste heat directly to space. Early radiation-cooled TWT configurations were not efficient, and the number of operating TWTs that a given satellite could accommodate was limited to some small number, such as five.
From the above, it can be envisioned that a TWT configuration which provides more efficient cooling, less weight, and higher power generation per transponder than prior art systems would be highly desirable. The present invention combines several techniques in a novel manner to provide a high power and energy efficient satellite based transmitter system. As a result, the output power of such a satellite is increased considerably without a proportional increase in size.